1. Field of the Invention
The present invention relates to a bed apparatus provided with a bed-departure prediction and detection system for determining bed-departure/bed-presence of elderly persons suffering from dementia, patients that have recently undergone surgery, or other persons, and for predicting bed-departure on the basis of the movement of a user on the bed, and particularly relates to a bed apparatus having a movable bedboard that performs a back-raising movement and/or a knee-raising movement.
2. Description of the Related Art
In recent years, wandering of elderly persons suffering from dementia and accidents involving stumbling and falling in the vicinity of the bed have become a social problem, and a solution to this problem is needed. There are high expectations thata quicker response can be achieved during an abnormal situation by monitoring the on-bed movements of elderly persons, patients that have recently undergone surgery, or other users who are bedridden over a long period of time, by using the load information of the bed.
The art disclosed in Japanese Laid-Open Patent Application No. 2-280733 merely uses load information to determine whether a user is still on the bed or has left the bed, and cannot monitor the movement of the user on the bed.
The arts disclosed in Japanese Patent Nos. 3093745 and 3322632, U.S. Pat. No. 5,276,432, and J. C. Barbenel et al., Monitoring the mobility of patients in bed, Medical & Biological Engineering & Computing, pp. 466-468 (September 1985) solve this problem by calculating the center of gravity from the weight information of four points on the bed, and uses the center-of-gravity position information to monitor the movement of a user in bed.
However, in Japanese Patent Nos. 3093745 and 3322632, and U.S. Pat. No. 5,276,432, even though the user can be determined to be at the edge of the bed, for example, by monitoring only information related to the center-of-gravity position of the user on the bed, it cannot be determined whether the user is at the edge of the bed due to turning over in bed or moving in another manner, whether the user is at the edge of the bed in an attempt to leave the bed, or whether the variations in the center-of-gravity position are due to an item being placed on the bed section in which the user is sleeping, or another non-user person leaning or sitting on the bed section. Also, there is a problem in that distinction cannot be made from a sit-up movement, and errant determinations may occur when the center of gravity has changed due to the railing or other accessory items being removed.
The art disclosed in J. C. Barbenel et al. is one in which the load of four bed legs is measured by load cells, and the body weight of the patient on a bed is measured in order to monitor the movement of a patient on the bed. The center of gravity on the bed is computed from the difference in the load measurement values of the bed legs, and the movement distance of the center of gravity is computed. Also disclosed is an art in which the state of the patient is determined from the number of movements of the patient on the bed.
However, in the art disclosed in J. C. Barbenel et al., there is a problem in that the movement of the user on the bed cannot be determined to be movement of the center of gravity that is caused by an item being placed on the bed section in which the user is sleeping, or another non-user person leaning or sitting on the bed section, because the movement of the user on the bed is measured by using only the movement distance of the center of gravity on the bed, and such a situation leads to errant determinations.
The prior arts described above have a problem in that a back bottom (back bedboard), a hip bottom (hip bedboard), and a knee bottom (knee bedboard), for example, are provided to the bed frame, the hip bottom is fixed to the frame, and the back bottom pivots about the center of the end section of the hip bottom side. False alarms are thereby generated and detection accuracy is reduced because the center of gravity varies when the back has been raised in a bed apparatus that is provided with a movable bedboard in which the back bottom is electrically raised. This is the same as in electric beds in which the knee bottom lifts the position of the knee when the knee bottom pivots about the center of the end section of the hip bottom side.
In this manner, there is a problem in that the center-of-gravity position of the bed user varies due to the back-raising movement and knee-raising movement in a conventional electric bed having a movable bedboard, and false alarms are generated indicating that the user has moved to a edge-sitting position and the detection accuracy of whether the bed user is at the edge of the bed or not is reduced regardless of whether the bed user has moved on the bed.